Page 306 - Anatomy and Physiology of Farm Animals, 8th Edition

Blood and Other Body Fluids / 291

Table 15-2. Representative Values for Blood Cell and Platelet Numbers
per Microliter of Blood in Selected Domestic Animals
VetBooks.ir Blood Element Horse Cow Dog Chicken

Erythrocytes 8–11 1 6–8 1 6–8 1 2.5–3 1
Total leukocytes 8–11 2 7–10 2 9–12.5 2 20–30 2
Neutrophils 4–7 2 2–3.5 2 6–8.5 2 5–10 2
Lymphocytes 2.5–4 2 4.5–6.5 2 2–3.5 2 11–18 2
Monocytes 400–500 350–500 450–600 2–3 2
Eosinophils 200–500 150–500 200–500 600–2,000
Basophils <100 <100 <100 200–900
Platelets 150–450 2 300–500 2 300–500 2 25–40 2
1 Millions.
2 Thousands.

Carbon dioxide also binds to hemoglobin Carboxyhemoglobin is a more stable
at a different site on the molecule. Carbon compound formed when carbon mon-
dioxide binds to α‐amino groups of peptide oxide combines with hemoglobin. The
chains to form carbaminohemoglobin. affinity of hemoglobin for carbon mon-
Binding of oxygen and carbon dioxide to oxide is 210 times that of its affinity for
hemoglobin is readily reversible. Blood O . The carboxyhemoglobin is unable to
2
arriving at the lungs from the peripheral carry oxygen, and the animal essentially
circulation contains carbaminohemoglobin suffocates, although the blood is typi-
and is exposed to air with a relatively high cally cherry red.
concentration of oxygen and a relatively low
concentration of carbon dioxide. In the Erythropoiesis and Degradation of
lungs, carbon dioxide dissociates from car- Erythrocytes. Erythrocyte formation,
baminohemoglobin, resulting in the forma- called erythropoiesis, is regulated by the
tion of hemoglobin, which can bind oxygen hormone erythropoietin, a glycoprotein
to become oxyhemoglobin. When the hormone that is released from specific
blood containing oxyhemoglobin returns cells of the kidneys in response to reduced
to the peripheral tissues that are relatively oxygen delivery. For example, when animals
deficient in oxygen, the bound oxygen is move from low altitudes to high altitudes,
released to the tissues. Carbon dioxide can where less oxygen is available, erythropoietin
then bind to hemoglobin to continue the release is increased. Erythropoietin acts
cycle. on stem cells in the bone marrow to
Methemoglobin is a true oxidation increase the production of erythrocytes.
product of hemoglobin that is unable to The increase in erythrocyte number is not
transport oxygen because the iron is in the immediate (it requires some days) because
2+
3+
ferric (Fe ) rather than the ferrous (Fe ) mature erythrocytes must be formed from
state. Certain chemicals, such as nitrites stimulated stem cells before release from
and chlorates, produce methemoglobine- the bone marrow. The larger number of
mia (methemoglobin in the blood). Nitrate erythrocytes increases oxygen delivery to
poisoning has been reported in cattle the kidneys, and this has a negative
grazing on highly fertilized plant growth. feedback effect on erythropoietin release.
In these cases, nitrates in the plants are It is via this feedback that a stable rate of
converted to nitrites in the rumen and erythrocyte production is maintained.
cause the formation of methemoglobin Recombinant human erythropoietin
when absorbed into the blood. (rhEPO) has been used in appropriate